1. Field of the Invention
The present invention relates to a pattern forming method for forming a pattern on an object, and a device production method. The present invention is applicable, for example, when a fine pattern, which is finer than the resolution limit of an exposure apparatus, is formed.
2. Description of the Related Art
When a device such as a semiconductor element or the like (electronic device, microdevice) is produced, a device production process is used, which includes repeating a thin film formation process for forming a thin film on a substrate such as a wafer, a glass substrate or the like, a lithography process for forming a resist pattern (pattern of a photosensitive material) on the substrate or the thin film, and a processing process for processing the substrate or the thin film by using the resist pattern as a mask. In this specification, the lithography process (lithography step) means a process which includes a coating step of coating the substrate with the resist (photoresist), an exposure step of exposing the resist via a mask pattern by using an exposure apparatus, and a development step of developing the resist after the exposure.
In response to the progress of the fine pattern of the semiconductor element or the like, those having been performed, in order to enhance the resolving power, with respect to the exposure apparatus to be used in the lithography process include, for example, the progress of the short wavelength for the exposure wavelength, the increase in the numerical aperture NA of the projection optical system, the optimization of the illumination condition including the so-called modified illumination, etc. and the development of the mask technique including the phase shift reticle, etc. Recently, an exposure apparatus, which uses the liquid immersion method, has been also developed in order to further increase the numerical aperture NA substantially while securing broad depth of focus. Recently, the so-called double process system is also suggested, in which the lithography process is repeated twice to thereby form a fine circuit pattern that exceeds the resolution limit of the exposure apparatus (see, for example, Japanese Patent Application Laid-open No. 2007-311508).
In the conventional pattern forming method of the double process system, it is necessary that the overlay exposure is performed in a second lithography process to be carried out a second time. Therefore, a problem arises such that the shape accuracy of the fine pattern to be finally formed depends also on the alignment accuracy of the exposure apparatus.